Not applicable.
The invention relates to drug delivery systems by which set doses may be apportioned from a cartridge and delivered, the dose setting being made by changing the relative position of cooperating dose setting elements and the delivery being made by pressing a button until it abuts a stop.
The deliverance may take place as an aerosol spray, an injection, or a high pressure jet which penetrates the skin so that the delivered material may be precipitated in the tissue beneath the skin.
The dose setting elements may be a threaded rod and a nut as in EP 327 910 wherein the threaded rod is a piston rod acting on a piston which presses out liquid from a cartridge in accordance with the distance the piston is moved. By dose setting a nut at the end of a hollow button surrounding a threaded piston rod is screwed along the piston rod away from a stop and thereby lifts the button up from the proximal end of the injection device. The injection is performed by pressing the button to move the nut back to the stop by which movement the piston rod and the piston is pressed into the cartridge a distance corresponding to the distance the nut was screwed away from the stop.
In another dose setting mechanism as described in WO 90/0038 a carrier, which may transport the piston rod in only a distal direction, is by the setting of a dose moved away from a stop and may thereafter by pressing an injection button be moved back to abutment with said stop.
In still another injection device as described in EP 0 245 312 a button with a push rod may be operated to reciprocate over a fixed distance. During part of its reciprocating movement the push rod drives a piston into a cartridge. Said part corresponds to a set dose which is set by varying a free space between the piston rod an the piston when the button and the push rod is in their not operated position.
The size of set doses is mainly indicated by a pointer or through a window which is coupled to one of the dose setting elements and indicates a number corresponding to the set dose on a scale coupled to the other dose setting element the size of the dose being proportional with the distance the two elements have been moved relative to each other. This fact sets a limit for the size of the figures on the scale although different initiatives has been taken to expand the space available for these figures. The dose setting is performed by turning a screw or a wheel or by rotating two parts of the injection device relative to each other and currently monitor the size of the dose set. By some constructions of the dose setting mechanism it is not possible to reduce the set dose if the two dose setting elements have been moved to far in relation to each other, i.e. if a too large dose has been set. By other constructions it is necessary to make sure that the device is reset before a dose can be set. A device which is very simple to use is aimed at. The simplest form of device should only show a very simple dose setting device and an injection button.
It is the object of the invention to provide a user-friendly injection device by which more of the known draw-backs are avoided.
This is obtained by an injection device as described in the opening of this specification, which device is characterized in that the dose setting is read in into an electronic circuit and the dose setting movement of the dose setting elements relative to each other is performed by an electromechanical device, e.g. a motor, controlled by the electronic circuit in accordance with the read in dose setting.
According to the invention the electronic circuit may appropriately comprise a microprocessor.
The use of an electric motor in an injection device is known but in such known devices the motor is used to perform the injection. However, it has appeared that it is preferable to make the injection manually as this gives the user the possibility of adjusting the injection speed in accordance with the absorption of the injected liquid in the tissue. Further it is rather power consuming to perform the injection movement and consequently the batteries which must have small physical dimensions will be exhausted very quickly.
Combining electronic control and electromechanical setting of a dose enables the apparatus to intervene actively if anomalous or unintended conditions are detected during a dose setting sequence or if a not allowed handling of the apparatus is detected, so as opening of the cartridge holder during the setting of a dose. The active intervention may comprise a resetting of the dose setting to a starting point corresponding to the dose =0 and then a reporting of a malfunction until the error has been corrected, e.g. by closing the cartridge holder. This way the risk for erroneous doses and the doubts whether a correct dose is delivered or not may be overcome. When the error has been corrected or the unintended handling of the apparatus has stopped, the setting of the dose may be restarted from the starting position of the apparatus.
An electronically setting of the dose be performed by using one or two buttons by which a counting up or a counting down of a dose may be ordered to an electronic circuit.
The set dose may currently be shown on an electronic display and the counting may be performed upwards as well as downwards. The use of an electronic display offer the advantage that the size of the figures in the display depends only on the size of the display. Also other presentation devices than a display may be used, e.g. a speech synthesizer circuit currently pronouncing the number corresponding to the set dose.
The setting may be obtained by reading the wanted dose into the electronic circuit which present the read in dose in the display an controls the motor to run in a direction to set the mechanic parts of the dose setting mechanism accordingly. When a signal from a position reader indicates that the mechanic parts has reached a position corresponding to the set dose the electronic circuit will cause a stop of the motor.
The motor may be able to perform the mechanical setting at about the same speed as the counting up or down is performed on the display. If the mechanical setting is not obtained or is unbearably delayed in relation to the showing of the display it is taken as an indication of exhausted batteries and an error is reported to the user, e.g. by switching of the display.
Alternatively the reading of the display may be a feed back from a position reader reading the size of the mutual movement of the dose setting elements. In this way it is ensured that the dose setting is in accordance with the reading on the display as this reading is an expression of the actual relative position of the dose setting parts. In this embodiment an exhausted battery will result in a very slow or failing counting in the display.
In known motor driven delivery systems a set dose may be shown in a display and a count down may be shown concomitant with the motor driven injection. However, except from the showing of the display the set dose is not visually recognizable. In opposition thereto the electromechanical setting according to the invention will ensure that the setting further is physically recognizable as the physical position of the dose setting parts relative to each other may be visually inspected.
A switch may be provided which is operated when the injection button is pressed home. The operation of the switch ensures that the injection button is in its zero position before a new dose setting may be performed.
A further advantage by the device according to the invention is that limits may be set as an information read into the electronic circuit. If a maximum dose must not be exceeded the circuit may be so programmed that a number higher than the maximum number of units of the drug to be delivered cannot be read in into the electronic circuit.
Also the circuit may be programmed to set a predetermined dose every time the dose setting is operated. This may be of importance to people who are themselves unable to perform the setting.
The movement of the dose setting elements are recorded to the electronic circuit and is translated to a number indicating the set dose in units defined for the sort of medicine which is administered by the injection device. As medicine may occur with different concentrations and as from one type of medicine to another different volumes may corresponds to a unit, it is advantageous that the translation of movement into units is made electronically so that the same mechanical device may be made useable for different types and concentrations of medicine just by a programming of the circuit. The programming of the circuit may co-operate with a code on the cartridge so that the program is automatically adapted to the medicine in the cartridge and the correct amount is delivered when a dose is set by its number of units.